Strain gauge pump control switch

ABSTRACT

A control switch incorporates a solid state transducer, a strain gauge. The transducer responds to a local environmental condition, such as fluid level, or pressure and exhibits a parameter change which can be detected as an electrical output. Control circuits coupled to the transducer can sense the parameter change and switch a source of electrical energy to a load in response thereto.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of the filing date of U.S.Provisional Application Ser. No. 60/939,453 filed May 22, 2007 andentitled “Strain Gauge Pump Switch”. The disclosure of the '453application is incorporated herein by reference.

FIELD

The invention pertains to solid state pump control switches. Moreparticularly, the invention pertains to such switches which incorporatea strain gauge as a transducer to convert an environment condition, suchas a level of a fluid, to an electrical signal.

BACKGROUND

Various types of switches have been developed for use in turning pumpson and off in response to an external ambient condition, such as waterlevel. Such switches tend to be used in relative harsh environments suchas in tanks of water, or, sump pits which are used to collect foundationwater. Other environments include industrial fluids which might becaustic or acidic, as well as high or low temperatures.

While known switches can be useful and function properly over a periodof time, they are always subject to failure. Switch failures in turntranslate into non-running pumps which can result in flooded commercial,industrial and residential locations. Alternately, non-running pumps canresult in water supply deficiencies, or failures to supply commercial orindustrial fluids for various applications.

One switch configuration has been disclosed in U.S. Pat. No. 7,307,538,issued Dec. 11, 2007, and entitled “Pump Connector System”. The '538patent is assigned to the assignee hereof and is incorporated herein byreference.

There is an on-going need for control switches usable in suchenvironments which exhibit greater reliability and longer lifetimes thando known switches. Preferably, such improved switches would be pricecompetitive with known switches and readily substitutable therefore.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of a switch assemblage in accordance with theinvention;

FIG. 2 is a side sectional view of an exemplary switch housing as inFIG. 1;

FIG. 3 is an end view of an embodiment of a transducer in accordancewith the invention; and

FIG. 4 is a block diagram of control circuits in accordance with anembodiment of the invention.

FIG. 4A is a perspective view of an electrical cable and AC connector inaccordance with the invention.

DETAILED DESCRIPTION

While embodiments of this invention can take many different forms,specific embodiments thereof are shown in the drawings and will bedescribed herein in detail with the understanding that the presentdisclosure is to be considered as an exemplification of the principlesof the invention, as well as the best mode of practicing same, and isnot intended to limit the invention to the specific embodimentillustrated.

Embodiments of the invention incorporate a strain gauge as a transducerto sense the presence of a fluid either through displacement, buoyancyof a structure or by fluid pressure deforming a strain gauge platform.Such embodiments can be implemented as solid state structures which canbe digitally calibrated for various settings or pressure.

In one aspect of the invention, such transducers can be coupled toelectronic control and switching circuitry which can switch electricalenergy to activate a load, such as an electric motor for a pump.Advantageously, motor starting inrush currents are diverted away fromthe transducers in such embodiments. Further, such transducers canaccurately respond to changing conditions, such as level or pressure,resist vibration and can withstand harsh operating environments.

The control and switching circuitry can include relatively high powersemiconductor switches which are controlled by one or more programmableprocessors which in turn are coupled to one or more solid statetransducers, preferable strain gauges. The processor(s) can digitallycalibrate one or more strain gauges.

In another aspect of the invention, a solid state switch, such as atriac, can be coupled in parallel with a relay to a pump motorconnector. The switch and relay can be independently controlled bycontrol circuits in the unit. In response to signals from the straingauge, the control circuits can bias the switch to a low impedance stateto couple electrical energy to the pump connector. In this state, theswitch can couple the motor start up, inrush, current without arcing orthe like to the pump connector to start the motor. Once the inrushcurrents have subsided, for example after a time interval such as two orthree seconds, the control circuits can activate the relay which changesstate and provides a closed contact pair to carry the motor current asan alternate to the solid state switch. The relay contacts shunt themotor current away from the switch enabling it to cool off as needed.

When the strain gauge indicates that the lower water level has beenreached, the control circuits de-energize, turn off, the relay whichopen circuits the motor current circuit through those contacts.Subsequently, after another time interval, such as two or three seconds,the solid state switch is biased off, or placed in a high impedancestate by the control circuits. When the switch turns off it, and not therelay contacts, absorbs any turn off current or voltage transients whichmight otherwise cause arcing at the relay contacts. Those contacts arethus protected from electro-ablation, contact burning.

With respect to FIGS. 1-4, a pump control system 10 includes a watertight housing 12 with an open end 12 a closed by a diaphragm 16. A ring14 is located in the housing 12 between the diaphragm 16 and a circuitboard 40. Housing 12 is placed in the sump along with a pump having amotor 24 to be switched on and off.

An electrical cable 20 couples housing 12 to a double sided AC connector22. Connector 22 carries a pump AC receptacle 22 a at one end and ACoutlet prongs 22 b at the other end. In operation, a pump AC connectoris plugged into receptacle 22 a. Prongs 22 b are plugged into a localutility supplied AC outlet.

The ring assembly 14 has an annular shape and with molded radial members14-1, -2, -3, and -4. Radial member 14-4 carries an elongated,deflectable, metal plate 32 which supports a strain gauge 34. A pressuresensing plate 28 carries a connector prong 30. A centered perforation 36in a free end of plate 32 receives the connector prong 30 with afriction fit and supports pressure plate 28 for axial motion in responseto applied fluid pressure.

A printed circuit board 40 carries sensing and control circuits 42.Surge suppressing circuits 44 are coupled to a DC supply 46. A digitalcircuit regulator 48 and analog circuit regulator 50 feed digitalcircuits 56 and differential amplifier 52 respectively.

The differential amplifier 52 is coupled to strain gauge 34 viaconnectors 34 a. Movement of the plate 28 in a first direction inresponse to increasing fluid pressure generates a signal of a firstpolarity at amplifier 52. Movement of plate 28 in the oppositedirection, in response to decreasing fluid pressure generates a signalof the opposite polarity at amplifier 52.

Digital control circuits 56 include a programmable processor or computer58 a, and associated storage, random access memory, EEPROM and Flashmemory indicated generally at 58 b. Software, or, control programsstored in EEPROM or Flash memory can be executed by processor 58 a incarrying out the above described switching process.

Circuits 56 can be accessed via a programming interface 58 e. A factorycalibration port 58 f is also provided.

Digital output circuits 58 c are respectively coupled to Triac driver 62a and Triac 62 b, and relay driver 64 a and relay 64 b. As describedabove, electrical energy from connector 22 is switched by Triac 62 b andrelay 64 b to provide a switched AC output 20 c which can be coupled topump motor 24 via pump receptacle end 22 a.

A vent tube 20 d extends from within housing 12, via cable 20 andterminates at connector 22. Tube 20 d maintains pressure in the housing12 at local atmospheric pressure.

From the foregoing, it will be observed that numerous variations andmodifications may be effected without departing from the spirit andscope of the invention. It is to be understood that no limitation withrespect to the specific apparatus illustrated herein is intended orshould be inferred. It is, of course, intended to cover by the appendedclaims all such modifications as fall within the scope of the claims.

The invention claimed is:
 1. A switch comprising: a housing having anopen end which defines an interior region; a ring having an annularshape and carried in the housing adjacent to the open end thereof, thering including molded members which extend radially toward the center ofthe ring; an elongated plate with first and second ends where one end ofthe plate is coupled to a radial member of the ring, and the other endof the plate has an opening, and is deflectable, a strain gauge iscarried on the plate and extends radially toward the opening in theplate; a cylindrical pressure plate with an axial connector prong whichengages the opening of the deflectable end with a friction fit and, inresponse to one of applied fluid level, or fluid pressure, the platemoves axially in a first direction, relative to the ring, to generate asignal of a first polarity at a selected electrical circuit, wherein thecircuit is carried in the housing with the strain gauge located betweenthe pressure plate and the circuit; an electrical port at a second endof the housing, displaced from the open end wherein a power cord with anend extends through the port and the end connects to the circuits, thepower cord includes a vent tube which extends from the housing to a freeend of the cord; and a diaphragm carried by the housing adjacent to thepressure plate, the diaphragm closes the open end of the housing whereinthe housing is water tight.
 2. A switch as in claim 1 where theelectrical circuit includes a solid state switching element connected inparallel with a relay to provide a motor starting current.
 3. A switchas in claim 1 where the free end carries a power input plug.
 4. A switchas in claim 3 where the plug has first and second spaced apart surfaceswith electrical prongs extending from the first surface and with anelectrical socket defined in the plug adjacent to the second surface. 5.A switch as in claim 4 where the prongs are adapted to receiveelectrical energy and the socket is adapted to be releasably connectableto an electrical load.
 6. A switch as in claim 5 where the circuit hasfirst and second states and switches therebetween in response tomovement of the plate when in the first state an electrical circuit iscompleted between at least one of the prongs in the socket.